title: Bactericidal activity of PA-824 against Mycobacterium tuberculosis under anaerobic conditions and computational analysis of its novel analogues against mutant Ddn receptor.
abstract: BACKGROUND
  The resurgence of multi-drug resistant tuberculosis (MDR-TB) and HIV associated tuberculosis (TB) are of serious global concern. To contain this situation, new anti-tuberculosis drugs and reduced treatment regimens are imperative. Recently, a nitroimidazole, PA-824, has been shown to be active against both replicating and non-replicating bacteria. It is activated by the enzyme Deazaflavin-dependent nitroreductase (Ddn) present in Mycobacterium tuberculosis which catalyzes the reduction of PA-824, resulting in the release of lethal reactive nitrogen species (RNS) within the bacteria. In this context, PA-824 was analyzed for its activity against latent tuberculosis under anaerobic conditions and compared with rifampicin (RIF) and pyrazinamide (PZA). Recent mutagenesis studies have identified A76E mutation which affects the above mentioned catalysis and leads to PA-824 resistance. Hence, novel analogues which could cope up with their binding to mutant Ddn receptor were also identified through this study.
  
  
  RESULTS
  PA-824 at an optimum concentration of 12.5 μg/ml showed enhanced bactericidal activity, resulting in 0 CFU/ml growth when compared to RIF and PZA at normal pH and anaerobic condition. Further docking studies revealed that a combinatorial structure of PA-824 conjugated with moxifloxacin (ligand 8) has the highest binding affinity with the wild type and mutant Ddn receptor.
  
  
  CONCLUSIONS
  PA-824 has been demonstrated to have better activity under anaerobic condition at 12.5 μg/ml, indicating an optimized dose that is required for overcoming the detoxifying mechanisms of M. tuberculosis and inducing its death. Further, the development of resistance through A76E mutation could be overcome through the in silico evolved ligand 8.
authors.affiliation: Foundation for Innovative New Diagnostics, Flat No, 6-14 (excluding No, 7), 9th floor, Vijaya Building, 17-Barakhamba Road, New Delhi 110 001, India. cn.paramasivan@finddiagnostics.org.
authors.forename: Sulochana
authors.initials: S
authors.lastname: Somasundaram
authors.forename: Ramaian Santhaseela
authors.initials: RS
authors.lastname: Anand
authors.forename: Perumal
authors.initials: P
authors.lastname: Venkatesan
authors.forename: Chinnambedu N
authors.initials: CN
authors.lastname: Paramasivan
mesh_terms: D000693:Anaerobiosis; D000995:Antitubercular Agents / Q000737:chemistry* / Q000494:pharmacology*; D015169:Colony Count, Microbial; D024881:Drug Resistance, Bacterial; D006801:Humans; D050296:Microbial Viability / Q000187:drug effects*; D062105:Molecular Docking Simulation; D050505:Mutant Proteins / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D009593:Nitroimidazoles / Q000737:chemistry* / Q000494:pharmacology*; D009601:Nitroreductases / Q000378:metabolism
chemical_list: D000995:Antitubercular Agents; D050505:Mutant Proteins; D009593:Nitroimidazoles; C410767:pretomanid; D009601:Nitroreductases